package bfsalgorithm;

import java.util.LinkedList;
import java.util.Queue;

/**
 * 130、被围绕的区域
 */
public class Exercise4 {
    int[] dx = {0,0,1,-1};
    int[] dy = {1,-1,0,0};
    int m;
    int n;

    public void solve(char[][] board) {
        m = board.length;
        n = board[0].length;

        for(int j = 0;j < n;j++) {
            if(board[0][j] == 'O') {
                bfs(board,0,j);
            }
            if(board[m - 1][j] == 'O') {
                bfs(board,m - 1,j);
            }
        }

        for(int i = 0;i < m;i++) {
            if(board[i][0] == 'O') {
                bfs(board,i,0);
            }
            if(board[i][n -1] == 'O') {
                bfs(board,i,n - 1);
            }
        }

        for(int i = 0;i < m;i++) {
            for(int j = 0;j < n;j++) {
                if(board[i][j] == '.') {
                    board[i][j] = 'O';
                }else if(board[i][j] == 'O') {
                    board[i][j] = 'X';
                }
            }
        }
    }

    public void bfs(char[][] board,int i,int j) {
        // 只有边界为‘O’才会进来
        Queue<int[]> heap = new LinkedList<>();
        heap.add(new int[]{i,j});
        board[i][j] = '.';

        while(!heap.isEmpty()) {
            int[] t = heap.poll();
            int a = t[0],b = t[1];
            for(int k = 0;k < 4;k++) {
                int x = a + dx[k];
                int y = b + dy[k];
                if(x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O') {
                    heap.add(new int[]{x,y});
                    board[x][y] = '.';
                }
            }
        }
    }
}
